Process for controlling porosity in fibrous webs

ABSTRACT

A PROCESS FOR CONTROLLING POROSITY IN FIBROUS WEBS. THE PROCESS INCLUDES A COMBINATION OF STEPS COMPRISING IMPARTING MOVEMENT TO A FIBROUS WEB SO AS TO PRESENT A MOVING SURFACE, DEPOSITING A SUBSTANTIALLY LIQUID MATERIAL ON THE MOVING SURFACE, EMBEDDING THE LIQUEFIED MATERIAL INTO CONTINUOUS PORTIONS OF THE MOVING SURFACE, AND APPLYING A FORCE EQUALLY ON EACH CONTINUOUS PORTION SIMULTANEOUSLY AND CONTINOUSLY WITH THE EMBEDDING STEP SO AS TO CAUSE ATTACHMENT OF ADDITIONAL LIQUEFIED MATERIAL WITH THE EMBEDDED MATERIAL. THIS PROCESS IS PARTICULARLY ADAPTED FOR MANUFACTURE OF PRODUCTS WHICH ARE USEFUL IN FILTERING GASES, CHEMICALS, AND LIQUIDS. WATERPROOF FABRICS HAVING AIR AND WATER-VAPOR PERMEABILITY MAY ALSO BE PRODUCED ACCORDING TO THE PROCESS.

July 20, 1971 J RUDMAN 7 3,594,213

' PROCESS FOR CONTROLLING POROSITY IN FIBROUS WEBS Filed Oct. 27, 1967//v VENTO/Z, JOSEPH [FUD/WW 44,745, W 4&4; fax-106M ATTOKNEYS UnitedStates Patent 3,594,213 PROCESS FOR CONTROLLING POROSITY IN FIBROUS WEBSJoseph T. Rudman, -51 Bay 25th St., Far Rockaway, N.Y. 11691 Filed Oct.27, 1967, Ser. No. 678,708 Int. Cl. B44d 1/44 U.S. Cl. 11765.2 12 ClaimsABSTRACT OF THE DISCLOSURE A process for controlling porosity in fibrouswebs. The process includes a combination of steps comprising impartingmovement to a fibrous web so as to present a moving surface, depositinga substantially liquid material on the moving surface, embedding theliquefied material into continuous portions of the moving surface, andapplying a force equally on each continuous portion simultaneously andcontinuously with the embedding step so as to cause attachment ofadditional liquefied material with the embedded material. This processis particularly adapted for manufacture of products which are useful infiltering gases, chemicals, and liquids. Waterproof fabrics having airand water-vapor permeability may also be produced according to theprocess.

DESCRIPTION OF PRIOR ART It is generally known that conventionalmechanical devices and methods used in coating and impregnating webssuch as paper, fabric, and the like, with liquid materials of variousviscosities, are not adaptable for obtaining uniform or controlledporosities in the webs. This is particularly true, for example, ofdevice-s and methods employing rotating rollers but it is also the casewith conventional doctor blade applicators. When rota-ting rollers areused, extreme accuracy of porosity control in the web becomes almost animpossibility because of the eccentricity of the periphery of the rollersurface, which usually cannot be held to less than .001 inch.

Virtually all of the conventional doctor blades are designed with anangle cut out of the bottom of the blade so that it terminates in asmooth and somewhat rounded edge over which the freshly coated web ismade to drag. The sliding action of web against the smooth edge seems toflatten down the coating and, in some cases, to cause somewhat of apenetration of the web, but these devices are incapable of controllingthe amount or distribution of the coating over the entire web orselected portions thereof. Also, because of the extremely short time inwhich the edge of such doctor blades is in contact with the web in thosecases where impregnation is important, it is extremely difficult to geta sufficiently deep penetration of the web structure. This isparticularly true when the Web in those cases where impregnation isimportant, it impregnant.

SUMMARY OF THE DISCLOSURE It is therefore an object of this invention toprovide an improved process for impregnating and/or coating fibrous websin which means are provided for controlling the porosity of the webs.

It is a further object of this invention to provide an improvedapparatus which is instrumental in obtaining said controlled porosity.

Another object of this invention is to provide a fabric which iswaterproof but also gas and water-vapor permeable.

Generally speaking, these and other objects of the present invention arerealized in a process for applying a liquefied material to a fibrousweb, the combination which 3,594,213 Patented July 20,, 1971 comprises,imparting movement to a fibrous web so as to present a moving surface,depositing a substantially liquid material on the moving surface,embedding the deposited material into continuous portions of the movingsurface and, applying a force equally on each continuous portionsimultaneously and continuously with the embedding step so as to causeattachment of additional liquefied material with said embedded material.

BRIEF DESCRIPTION OF THE DRAWING Further illustration of the presentinvention can be had by reference to the accompanying drawing.

FIG. 1 is a side elevational view of the coating and impregnatingapparatus of this invention.

FIG. 2 is a side cross-sectional view of the apparatus shown in FIG. 1.

FIG. 3 is an enlarged fragmentary cross-sectional view of a meteringblade, such as used in the invention, showing its contact with themoving web.

FIG. 4 shows an enlarged plan view of a blade means used in anotherembodiment of the invention.

In FIG. 1, a fabric web 1 is moved in a lateral direction by rotatingrollers 2. A frame 3 supports a metering blade 4 which is effective inimpregnating and/or coating the web with a coating material 5. Infraredlamps 6 serve to dry the fabric after it has been impregnated with thecoating solution.

FIG. 2 substantially shows a cross-sectional view of the apparatus shownin FIG. 1. The rollers 2 move the fabric 1 in a horizontal plane. Acoating solution 5 is permitted to drop from a reservoir 7 onto thefabric which then passes under the metering blade 4 to effectimpregnation. Generally, in order to effect an impregnation which is notvisible on the fabric, a metering blade having a contact width ofbetween 5 and mils will be necessary.

FIG. 3 shows an enlarged cross-sectional view of the metering blade 4.The leading edge 8 of the blade embeds the coating solution 6 in thefabric. The leading or upstream edge of the blade will have a keenconfiguration. The front side of the blade will be at a substantiallyright angle to the upstream edge. As used herein a substantially rightangle includes both acute and obtuse angles. The contact width 9 of theblade forces a controlled amount of additional coating material into theinterstices of the fabric in addition to the initially embeddedsolution. The contact width of the blade determines the amount ofadditional material forced into the fabric.

. FIG. 4 shows metering blade 10 having a gradient contact width 11.Such a blade is effective indepositing controlled but varied amounts ofcoating material across the width of a fabric. For example, that portionof the blade having a narrow contact width will deposit less coatingmaterial than the broader contact width portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As previouslymentioned the present invention relates to an improved process forcoating and impregnating fibrous webs.

In general, any substantially liquefied coating material may be used inthe invention.

Illustrative examples of polymeric materials which can be used as thecoating material are butadiene polymers including copolymers ofbutadiene with acryonitrile, styrene, acid esters of acrylic acid, anddiisocyanatelinked condensation elastomers such as urethanes,polyurethanes, for example those resulting from the reaction of toluenediisocyanate with relatively short linear polyester molecules, andmodified polyurethanes.

Organosilicon compositions which may also be used as the coatingmaterial include, for example, monomeric silanes such asdimethyldichlorosilane, octadecyltriacetoxysilane,trimethylchlorosilane, vinyldiisopropoxysilane, andphenylmethyldimethoxysilane; polymeric silanes such as methylsilazanes,methylpolysilanes containing Si-Si linkages such as dimethyltetramethoxysilane and silcarbanes such as Me (C H O)SiCHgSi(OC H )Meand siloxanes such as methylhydrogensiloxane, dimethylsiloxane,monomethylsiloxane, octadecylmethyl siloxane, octadecylhydrogensiloxane,phenylhydrogensiloxane and mixtures and copolymers of dimethylsiloxaneand methylhydrogensiloxane, ethylhydrogensilo-xane andtrimethylsiloxanes; and alkali metal salts of organosilanols such asMeSi(ONa) EtSiO (OK) C H SiOOLi, and mixtures thereof.

In several cases an oil or stain-repellant compound may be employedeither alone or along with another coating such as for example awater-repellent coating. Illustrative examples of such repellentsubstances include fluorochemical compounds such as those defined inU.S. Pats. 2,642,416; 2,826,564; 2,839,513; and 2,803,615. Otherfiuorochemical compounds which can be employed include the chromiumcoordination complexes of saturated perfiuoromonocarboxylic acids andperfluorooctanoic acid.

Fluoroc'hemical compounds suitable for use herein are availablecommercially, for example, those marketed under the trade nameScotchgard such as Scotchgard FC205 and FC208 and Zepel. Of thesecompounds, the Scotchgard FC205 and FC208 products, which are availablein emulsion form, may be described according to U.S. Pat. 2,803,615 bythe following general formula:

a F3C(CF2)XSOQN-RZOCO=CHZ in which x is a value between 3 and 13inclusive, R is a lower alkyl, such as methyl, ethyl, propyl, and thelike, having 1-6 carbon atoms. R is an alkylene containing 1-12 carbonatoms and R is H, methyl or ethyl.

The product Zepel is also available in emulsion form and while it ischemically different from the Scotchgard products, it is afluorochemical oil repellent containing fluorocarbon tails composed ofCF groups which may end in a terminal CF group.

Generally speaking, fiuorochemical compounds of the type indicated (e.g.Scotchgard) are known to demonstrate a water repellent effect but theyare not considered to be waterproofing materials. Nevertheless whenemployed in the treatment of fabrics as described in the process of thepresent invention superior waterproofing results are achieved.

Compounds imparting crease resistant properties to treated fabrics mayalso be used in this invention. Compounds of this type are described inU.S. Pats. 2,517,750; 2,825,732; 2,974,432; and 3,049,446.

Water-swellable hydrophilic elastomers such as for example thosedescribed in U.S. 3,265,529 may also be used in the invention. Othercompounds such as plasticizers, pigments, curing agents, soil releaseagents, etc. may also be added to the coating mixture or solution.

It will be recognized that the invention is applicable broadly to anyand all webs or fabrics comprising natural and/or synthetic fibers, e.g.cotton, rayon, glass, nylon, polyester (polyethylene terephthalate),acrylics, viscose, cellulose esters (e.g. cellulose acetate) celluloseethers, asbestos, flax, hemp, wool paper and so on.

The conditions used for drying and/or curing the web after applicationof the coating material will vary depending on the structure of thefabric and the nature of P the material used. Usually, however, thetemperature of drying is in the range between about 200-300 degrees F.for 1-10 minutes. When curing isrequired, exposure to temperaturesbetween about 250-375 degrees for an additional 1-10 minutes will benecessary. The temperature of the cure is determined by the propertiesof the fiber in th web and/or the nature of the applied coatingmaterial.

The coating material will generally be applied tothe Web from asolution, dispersion, or emulsion in which the liquid medium may bewater or an organic liquid may be used. Since the organic solvent is notcritical, it may be chosen from any number of organic solvents which arecommercially available and economically feasible for use in the process.However, it should be emphasized that the organic liquid must be inertin relation to the web and the coating material itself. A preferredsolvent is Varsol although other vehicles which may be used includexylene, toluene, benzene, heptane, butylacetate, trichloroethylene,Cellosolve, perchlorethylene, methylethylketone or any other solventwhich is compatible with the coating material. Cellosolve is the tradedesignation for 2-ethoxyethanol and is commercially available from UnionCarbide Corporation. Varsol is the trade designation for a straightpetroleum aliphatic solvent and is commercially available from theStandard Oil Co. of New Jersey.

The process of the present invention is particularly adapted for themanufacture of products which are useful in filtering gases, solids,chemicals, and/or liquids.

In one particular embodiment of the invention, cigarette filters may beproduced. Generally the porosity of such filters will be controlledaccording to the degree and type of filtration desired. For example, theamount of nicotine and tars which may be removed from the cigarettesmoke can be regulated to a substantial degree by controlling theporosity of the filter. This may be accomplished by means of a pluralityof filters or a single filter. According to the process of thisinvention such filters may be produced, for example, from paper orfabric and will generally be cut to the desired size and supported by around frame which is fitted in the cylindrical body of the cigarette.

Another product having controlled air porosity produced according tothis invention is parachute fabric. The porosity of such fabricgenerally is a factor in determining the parachutes rate of descent. Airporosity in such a fabric may be controlled to as low a degree as desirebut is limited, of course, in its maximum degree by the type of weaveemployed in the fabric.

When polyester/ cotton, polyester/rayon and polyester fabrics areintended for a particular application, a problem of major concern is thedifficulty of removing oily stains, food stains and soil therefrom. Theoil staining problem of polyesters is due in part to the smooth surfaceof the fiber. Because of its smoothness the fiber can act as a wick foroils. Added to this is the oleophilic nature of the polyester fiberitself. According to the process of this invention, any of theconventional soil release materials such as polyurethane or acrylicemulsions may be applied to an underlying fabric and will retain itssoil releasing properties even after multiple home launderings and drycleanings. The soil release finish may be applied in conjunction withwrinkle free materials or waterproofing compounds.

One of the more important products produced according to this inventionis an impregnated fabric, suitable for use as rainwear, which isbreathable and waterproof and also demonstrates a highly desirablefabric hand and appearance. This may be achieved by treating a basicfabric with a waterproof material, either hydrophobic or hydrophilic,according to the process of this invention such as previously described.The basic fabric which is to be made waterproof may have been treatedprevious to the process of this invention such as previously described.The basic fabric which is to be made waterproof may have been treatedprevious to the process of this invention with a thermosetting resinsuch as used in the wrinkle free fabrics. Such fabrics are commonly soldunder the trade names Perma-Press, and Koratron. Perma-Press is a tradedesignation for a coated fabric having permanent press properties, saidcoating being Permafresh 183 which is a trade designation for acarbamate chemical and which is commercially available from Sun ChemicalCorporation. Perma-Press is commercially available from Sears Roebuckand C0. Koratron is a trade designation for a coated fabric havingpermanent press properties, said coating being Permafresh 183. Thefabric may also have been previously treated with an oil or stainrepellent compound such as previously described herein.

It should be emphasized that the order in which the underlying web isimpregnated is not particularly important to obtain the resultsintended. For example, a fluorochemical impregnant can be applied undera polyurethane impregnant and still render the fabric resistant tostains. It should also be emphasized that the impregnants applied to theunderlying webs according to this invention remain fast in the web evenafter repeated washings or dry cleanings.

Rainwear fabric made according to this invention can be launderedrepeatedly in conventional washing machines without damage to itsresistance to water. It can also be dry cleaned with the usual drycleaning fluids such as perchlorethylene, and remains supple andwater-vapor permeable even during extended use.

With the present method the natural voids formed by the interstices ofthe web or fabric are filled so that microscopic voids are achieved.However, perhaps the most important fact of this method is that controlof such voids is achieved. In the absence of indication to the contraryall proportions are expressed on weight basis.

The following examples will further illustrate the invention.

EXAMPLE 1 A test fabric composed of 75% Dacron, 25% Avril fibers wastested at 3 locations for air porosity along its width. Dacron is thetrade designation for the condensation product of terephthalic acid andethylene glycol,

A 65/35 Dacron/cotton fabric was treated according to the process ofthis invention, with the modified polyurethane solution used in Example1 except in this case the solution had a viscosity of 10,000 cps. Adifferent metering blade was used to treat the test specimens. Specimen1 was treated with a blade having a contact width of 19 mils, specimen 2with a blade having a contact width of 11 mils, and specimen 3 withanother blade having a contact width of 40 mils. The varying airporosity achieved by the use of these different metering blades arenoted below in Table 2.

TABLE2 Air porosity, Specimen: cu. ft./min. 1 1.1

EXAMPLE 3 A 65% Dacron polyester cotton rainwear fabric previouslytreated with Scotchgard 205 resin and a urea was placed in an apparatussimilar to that illustrated in FIG. 1. The urea previously treated tothe fabric was an organic compound having more than one NH group permolecule and aided in waterproofing the fabric. This treated fabric(specimen 1 below) was coated with a solids solution. The metering bladeused in the process had a contact width of 11 mils but no open angle. Atthe same time a control sample (specimen 2) of the same fabric wascoated with the same modified polyurethane solution. The control samplewas coated on the sample apparatus; however, a A1. inch knife having an8 degree open angle was substituted for the 11 mil blade of specimen 1.After coating, the specimens were tested for air porosity, cured in anoven at a temperature of 300 degrees F. for 3 minutes and tested forwater resistance. The results are indicated below in Table 3.

TABLE 3 Air porosity Weight, g. Appearance after Rain test 1 (gms.coating Before After Before After water penetration) Specimen 1Invisible 8. 0 1. 42 5. 7 6. 2 0.2 g./10 min. Specimen 2 Slightlyvisible 8.0 0.82 5. 7 6.5 Saturated at 3 min.

1 Slowinskl Rain Test: 6 feet head for 10 minutes.

which is subsequently polymerized, and is commercially available from E.I. du Pont de Nemours & Co., Inc. Avril is the trade designation for amodified viscose rayon fiber having a high strength and is commerciallyavailable from American Viscose Co. Air porosity was tested on a Frazierapparatus. The same fabric was treated according to the process of thisinvention with a modified polyurethane manufactured and sold by HookerChemical Corp. under the trade name Rucothane C0-75. The polyurethanewas dissolved in a methyl ethyl ketone-toluol 50) solvent resulting in asolution having a viscosity of 20,000 cp. and air porosity results ofthe same three locations along the width of the fabric were noted. Thevariance in porosity in the control specimens as opposed to that in thetreated fabric is shown in Table 1 below.

TABLE 1.AIR POROSITY, CU. FTJMIN.

Location 1 Location 2 Location 3 ControL 12 15. 5 22 Treated 0.09 0. 100. 1O

EXAMPLE 2 The beneficial effect resulting from the use of the presentinvention is readily apparent from the above example. Thus specimen 2failed the waterproof test at 3 min. Specimen l was more than successfulin passing the waterproof test yet it maintained good air porosity. Itwas found that the fabric treated as specimen 1 is durable to launderingand dry cleaning and maintains a relatively soft hand.

EXAMPLE 4 TABLE 4 Oil repellency Oil repellency after three drycleanings- Slowinski Rain Test (3 ft. head/5 min.) Gms. water absorbed(6 it. head/10 min.)

After 3 dry cleanings (6 it. head/l0 min.) After 3 launderings (6 it.head/l0 Inin Moisture transmission (gmsJsq. it./hr.)

After 3 dry cleanings After 3 launderings 1 Saturated.

This example amply illustrates the superior results achieved by usingthe blade described in the present invention. Particularly astoundingare the results noted in the Slowinski Rain Test before and aftersuccessive launderings. The moisture transmission results indicated thatthe improved impregnation obtained with the process of this inventionstabilizes the fabric and minimizes residual shrinkage after launderingand dry-cleaning.

EXAMPLE 5 This example illustrates the vastly superior waterproofingproperties which are realized in using the present invention even whenthe test specimens ultimately have the same air porosity.

Two specimens were prepared from the same fabric comprising a 65/35blend of Dacron and cotton. Both specimens were coated with a modifiedpolyurethane methylethylketone solution having a 20% solids content.Specimen 1 was impregnated with a A inch blade having an 8 degree openangle. Specimen 2 was impregnated with an 11 mil blade with no openangle. The specimens were cured in an oven at 300 degrees F. andsubjected to the Slowinski Rain Test. The results are indicated below inTable 5.

TABLE 5.Cntinuerl Gms. of water Air absorbed (6 it.

porosity head/10 min.)

Specimen 1 2. 7. 0 Specimen 2 2. 5 0.7

EXAMPLE 6 This example shows the results achieved when a fabric istreated according to this invention with a soil release agent as well asa waterproof agent. A Dacron polyester 2-ply warp fabric having a singlefill was treated with a modified polurethane methylethylketone solutionsuch as utilized in Example 1 having a viscosity of 20,000 centipoises.The treated fabric contained 1 oz./sq. yd, of the modified polyurethaneafter drying at 180 degrees F. for one minute. A second impregnation wasmade of a silicone material sold by the Dow Corning Corp. under itstrade name FC-227. The silicone material had a viscosity of 25,000centipoises. The silicone impregnation was made on the same surface ofthe fabric and in the same manner as was the modified polyurethanesolution. The treated fabric was then cured at a temperature of 300degrees F. for one minute. The resulting fabric contained oz./sq. yd. ofthe silicone material. The fabric was divided into test specimens andwas spotted with various soiling substances such as mustard, oil, ink,etc. In all cases the fabric specimens were machine washed using Tidedetergent. The test specimens were then dried and examined for soilretention. In all cases miminal traces of soil remained.

{Fhe following standard test methods are referred to in the foregoingdescription.

Shower Rain Storm Waterproof lleight of column 2ft 2ft 1, 3 it (5ft.Time of exposure. 30 sec. 2 1ni11 5 min..." min.

8 Air permeability-Frazier method ASTM D-737-46 Moisture transmissionTest specimen is sealed to top of metal container measuring 2 /2 inchesin diameter by 2 inches in depth. The lower surface of the specimencontacts an absorbent wick which is approximately .05 inches thick byinch wide. The wick extends to the base of the container which containscc. of Water. The container is weighed and is then suspended in an ovenheld at 85 degrees F. for six hours. Weight loss is recorded. Resultsare shown in terms of moisture transmission in grams per square foot perhour.

What is claimed is:

1. A process for applying a liquefied coating material to a fibrous webwhich comprises:

(a) imparting movement to a fibrous web to present a moving surface;

(b) depositing said liquefied coating material on said moving surface, aportion of said liquefied coating material being embedded in the voidsof said moving fibrous 'web immediately upon being deposited upon saidmoving surface;

(c) applying by means of a metering blade a force equally on said movingsurface simultaneously and continuously with said depositing step at apoint on said moving surface immediately adjacent to and downstream ofthe point on said moving surface where said liquefied coating materialis being deposited on said moving surface, said metering blade having akeen upstream edge and a downstream edge defining a continuous,essentially horizontal fiat, webcontact, metering surface therebetween,said fiat metering surface being substantially parallel to and incontact with said moving fibrous web, said flat iweb-contact meteringsurface of said metering blade having a width between 5 and mils, saidarea of said metering surface of said metering blade contacting saidmoving fibrous web extending uninterrupted across said moving surface,and said moving fibrous web being unsupported at or near the area ofcontact with said metering surface of said metering blade, whereby saidmoving surface is depressed in the area where said force is beingapplied, whereby additional liquefied coating material is embedded inthe voids of said moving fibrous web and whereby the total amount ofliquefied coating material in the voids of the web is controlled by thewidth of the surface area where said force is being applied; and

(d) drying the liquefied coating material to thereby obtain a web havingcontrolled porosity.

2. A process according to claim 1 wherein said liquefied coatingmaterial is a modified polyurethane resin.

3. A process according to claim 1 wherein said fibrous web is a fabriccomprised of synthetic polymeric fibers.

4. A process according to claim 1 wherein said synthetic polymericfibers are polyester fibers.

5. A process according to claim 1 wherein said fibrous web is a fabricwhich comprises a blend of synthetic polymeric fibers and naturalfibers.

6. A process as described in claim 1 wherein said width of said surfacearea where said force is being applied is variable.

7. A process as described in claim 1 wherein said coated liquefiedcoating material is cured after the drying step.

8. A process as described in claim 1 wherein said liquefied coatingmaterial is a liquefied water-proofing coating material.

9. A process as defined in claim 8 wherein the waterproofing material isa hydrophobic compound.

10. A process as defined in claim 8 wherein the fabric has beenpreviously coated with fiuorochemical material.

11. A process as defined in claim 8 wherein the fabric has beenpreviously treated with a soil release agent.

9 10 12. A process as defined in claim 8 wherein the fabric 3,326,713 6/1967 Smith et a1. 11776 has been previously treated with a creaseresistant mate- 3,350,218 10/ 1967 Cagliardi 117--7 6 rial. 3,352,70611/1967 Alkofer 1171l1X References Cited 2,534,320 12/ 1950 Taylor118-413 371,155 10/1887 Videto 11s 41s m 2,271,458 1/19-42 Lionne 117111 FOREIGN PATENTS 2,423,555 7/1947 Ender 1171 11 456,377 11/1936 GreatBritain 117-1 11 2,632,422 3/1953 Elkins 11=8415 10 2,861,009 11/1958Rubner 118 415X WILLIAM D. MARTIN, Primary Examiner 2,989,422 6/ 1961Helbing 117-11l 3,000,760 9/1961 Gremer 117111 M. R. LUSIGNAN, AsslstantExammer 3,222,209 12/196-5 Brundige et a1. 117-e4 3,265,529 8/1966Caldwell et a1. 117-111X 15 117.7 111, 13 33, 1394, 1395, 143 13,302,610 2/1967 Mahoney 117--111X

